The present invention, in some embodiments thereof, relates to an isolated polypeptide of CD44 and, more particularly, but not exclusively, to an isolated polypeptide of CD44vRA and its use in the treatment of inflammatory disease.
CD44 is a cell surface adhesion molecule involved in multiple cellular functions, including cell-cell and cell-matrix interactions, cell migration, programmed cell death (apoptosis), or, conversely, cell survival and proliferation.
CD44 is the major cell surface receptor for hyaluronic acid (HA) but it has also been shown to bind proteins such as collagens, fibronectin, fibrinogen, laminin, mucosal vascular addressin and osteopontin. CD44 is essential for recruitment of circulating lymphocytes to the site of inflammation and marked accumulation of CD44, and sometimes hyaluronic acid, is detected in areas of intensive cell migration and cell proliferation, as in wound healing, tissue remodeling, inflammation, morphogenesis and carcinogenesis.
The genomic sequence of mouse and human CD44 includes 5 constant exons at the 5′ terminus, and 5 constant exons at the 3′ end. The mouse CD44 gene includes 10 variant exons in the middle of the molecule, designated V1-V10, resulting in a total of 20 exons. The human CD44 gene comprises only 9 of these 10 variant exons (V2-V10) thus comprising a total of 19 exons. Differential V2-V10 alternative splicing generates many isoforms of CD44 that express various combinations of variant exons (designated exon Vx, x=1-10), which are inserted in the membrane proximal domain and constitute the variable region of the molecule. These molecules are designated CD44 variants (CD44v). A few dozens isoforms of CD44 are known to date.
CD44s, which does not contain any variant exon, is the most ubiquitous form and is expressed by most cell types [Ponta, H., et al. Nat Rev Mol Cell Biol. 2003 January; 4(1):33-45]. CD44 variant proteins, in which one or more of the 10 variant exons are included, are mostly reported in association with cancer, and autoimmune diseases such as rheumatoid arthritis and multiple sclerosis [see e.g. Naor et al. Adv. Cancer Res., 71, 241-319, 1997; and Naor et al. Critical Reviews in Clinical Laboratory Sciences. 39, 527-579, 2002].
Joint inflammatory cells of patients with rheumatoid arthritis (RA) display a sequence of alternatively spliced CD44 variant designated CD44vRA. Human CD44vRA contains the same sequence as that of keratinocytes CD44v3-v10 isoform with an addition of extra alanine in the splicing junction between variant exon 4 and variant exon 5, which does not interfere with the reading frame. Mice with collagen-induced arthritis (CIA) contain at the same site a similar sequence that also includes the alanine. The CD44vRA sequence is expressed on joint inflammatory synovial cells of RA patients and Psoriatic Arthritis (PA) patients, but neither on keratinocytes nor peripheral blood leukocytes (PBLs) of healthy donors. Furthermore, while joint inflammatory cells of RA patients express CD44vRA, PBLs from the same patients and synovial fluid cells from osteoarthritis patients hardly express this variant, demonstrating the exclusivity of this isoform. (Nedvetzki et al., J Clin Invest 111:1211-1220, 2003; Golan et al., J Autoimm 28:99-113, 2007).
It has been reported that administration of anti-CD44 antibodies, CD44 proteins, peptides or derivatives can be used for treating various autoimmune diseases (e.g. Naor et al., Adv. Cancer Res., 71, 241-319, 1997; Naor et al., Critical Reviews in Clinical Laboratory Sciences. 39, 527-579, 2002; Turley E A, and Naor D. Front Biosci. 17:1775-1794, 2012). In addition, anti-CD44vRA monoclonal antibodies and CD44vRA-derived peptides were previously suggested (Golan et al., J Autoimm 28:99-113, 2007, International Application Publication Nos: WO2010/058396, WO 2005/007700; WO 2003/014160, WO 2000/075312; U.S. Pat. Nos. 7,534,605 and 8,193,311; and US Patent Application Publication No: US 20060019340).